Redded out, Yellowed out.

Redded out means that the AI will never trade this with you. I think that there should be a yellowed out to indicate that they would, but you don't have anything to give them.

That's easy to see, if it's normal colored but you have nothing to trade, then there's not going to be a trade. It's either a go/no go situation. If it's red it means they are either working on the wonder associated with it or don't want to trade it to you, whether they don't like you or think you are getting too advanced.

I mean you have things, but you don't have anything substantial to trade them for that particular item.